The present invention relates to narrow-profile, terminal block relays and in particular to a method of adding electrical fuses to such relays.
xe2x80x9cEuropean stylexe2x80x9d terminal blocks provide a method of electrical interconnection of industrial control components. These terminal blocks have a narrow and flat shape that allows them to be stacked together in close proximity when mounted on a DIN rail. When so stacked, wires may be received at terminals along the upper and lower edge of the terminal blocks.
The terminals allow connection to other wires connected to other terminals or to the leads of electrical components supported by the terminal block. Such electrical components may include fuses, indicator lights, and relays.
For a terminal block holding a relay (xe2x80x9ca terminal block relayxe2x80x9d) or a fuse (xe2x80x9ca terminal block fusexe2x80x9d), the relay or fuse is typically received by a socket at the front edge of the terminal block. The housings holding the relay or fuse are designed to have a width no greater than that of the terminal block, typically between 5 to 14 mm, to minimize space occupied on the DIN rail.
Programmable logic controllers (PLCs) are industrial computers used for the control of machines and processes. A PLC has input and output circuits that may connect to sensors and actuators on controlled machines and by executing a standard control language, such as relay ladder language, the PLC may read the inputs and according to the execution of the control program, provide outputs controlling the machine.
Terminal block relays are often used with a PLC, the latter which may be attached to the same DIN mounting rail on which the terminal block relays are mounted. Outputs from the PLC are connected to the coils of terminal block relays whose contacts in turn connect to the desired machine actuator to provide a form of isolation.
When the contacts of a terminal block relay are connected, for example, to an inductive load, a fuse may be placed in series with those contacts. This normally entails placing a fuse terminal block adjacent to each terminal block relay doubling the required space needed on the mounting rail. When many outputs to inductive loads are required, the amount of space on the rail is quickly exhausted.
The present invention provides a fuse adapter for adding a fuse to a terminal block relay without using additional space on the mounting rail. The fuse adapter also minimizes the wiring required to add a fuse to a terminal block relay.
Generally, the fuse adapter has a narrow housing holding a fuse and providing a conductive extension that may engage a terminal of the terminal block relay to mechanically and electrically fix the fuse adapter to the terminal block. When so fixed, the fuse adapter lies within the width of the terminal block relay so as not to interfere with adjacent terminal blocks. The fuse adapter provides an additional terminal that may receive a wire to connect the internal fuse in series between the received wire and the conductive extension. The fuse adapter also has the benefit of allowing the fuse to be replaced in the future, by providing a means of entry to the fuse adapter in the event it xe2x80x98openxe2x80x9d or warrants replacement in the circuit.
Specifically then, the present invention provides an in-plane fuse adapter for use with a terminal block relay, the terminal block relay being of a type mountable at its rear surface on a laterally extending rail to present a substantially constant lateral thickness between left and right planar walls each which may abut corresponding planar walls of adjacent terminal blocks mounted on the rail. The terminal block relay may provide a plurality of terminals accessible at upper and lower edges of the terminal block relay for receiving electrical connectors communicating electrical signals to a relay of the terminal block relay.
The fuse adapter comprises an insulating housing supporting a fuse holder within the housing. The fuse holder has a first and second socket receiving corresponding ends of a standard electrical fuse.
The fuse 64 may be replaced by prying it away from the sockets 60 and 66, which provide a spring clamping through their metallic elements.
A conductive extension is connected at a first end within the housing to the first socket. A second end of the conductive extension extends from the housing in an engagement direction so that it may be received and retained by a terminal of the terminal block relay. A wire terminal is supported by the housing and attached to the second socket so that it may receive and retain an external electrical conductor of a type normally received by the terminals of the terminal block relay. When the conductive extension is retained by a terminal of the terminal block relay, the housing lies substantially between planes of the left and right planar walls of the terminal block relay.
Thus, it is one object of the invention to provide a method of adding a fuse to a terminal block relay without using additional space along the mounting rail.
It is yet another object of the invention to provide a method of adding a fuse to a terminal block relay that reduces the number of terminal connections that must be made and eliminates a jumper. The present invention requires only two terminal attachments compared to three terminal attachments required when a jumper is used between a terminal block fuse and a terminal block relay.
It is yet another object of the invention to provide a convenient system for isolating outputs of programmable logic controllers using fuses and relays.
When the conductive extension is attached to a conventional terminal block relay, the left and right walls of the housing of the in-plane fuse adapter may be co-planar with the left and right planar walls of the terminal block relay.
Thus, it is another object of the invention to provide an assembled unit that retains substantially planar left and right walls minimizing areas that could catch debris or interfere with wiring operations.
The housing of the fuse adapter may include at least two retention surfaces that are not parallel to each other and that abut corresponding surfaces of the terminal block relay to resist torsion of the fuse adapter when it is installed in the terminal block relay. Alternatively or in addition, the housing of the fuse adapter may include a key portion fitting within a corresponding keyway of the terminal block relay to resist torsion of the fuse adapter with respect to the terminal block relay.
Thus, it is an object of the invention to provide a fuse adapter providing improved mechanical termination of a connecting wire.
The wire terminal may be positioned in the housing of the fuse adapter to receive an external electrical conductor along the engagement direction.
Thus, it is another object of the invention to allow wiring of the terminal block along the same axis and in a manner similar to that which would be used without the fuse adapter.
The wire terminal may operate to releasably retain the electrical conductor and in one embodiment, may be a screw and clamp terminal.
Thus, it is another object of the invention to preserve the benefits of being able to rewire the terminal block relay.
The extension may include a surface embossment.
It is therefore another object of the invention to provide increased mechanical retention of the fuse adapter as well as electrical connection.
The housing of the fuse adapter may include a door, or a hinged lever, providing access to the fuse holder.
It is thus another object of the invention to allow the fuse to be replaced without affecting the mechanical integrity of the connection between the wire and the terminal block relay.
The first and second socket of the fuse holder may be opposed about an access perpendicular to the extension direction and parallel to the left and right planar wall of the terminal block relay when the conductive extension is retained by a terminal of the terminal block relay.
Thus, it is another object of the invention to accommodate standard glass fuses without unduly increasing the cantilever of the fuse adapter.
The substantially constant lateral thickness of the terminal block is in most cases 6.2 mm.
Thus, it is another object of the invention to provide a system that works with standard European-type terminal blocks.
The fuse adapter may include an indicator lamp connected electrically in parallel with the sockets to light when the fuse is absent or open. The lamp may be an LED or neon and may be exposed through the housing along a front edge of the housing away from the rail when the conductive extension is retained by a terminal of the terminal block relay.
Thus, it is another object of the invention to provide a fuse adapter that provides features normally found in a terminal block fuse.
These particular objects and advantages may apply to only some embodiments falling within the claims and thus do not define the scope of the invention.